This invention relates generally to an exhaust gas recirculation system in an internal combustion engine, and more particularly to a control valve for controlling the mass flow rate of the recirculated exhaust gas in such a system.
Many of the current internal combustion engines, particularly those which are installed on automobiles, are equipped with a system for recirculating a portion of exhaust gas from the exhaust system to the intake system of the engine for the purpose of reducing the concentrations of oxides of nitrogen in the exhaust gas. It is a usual practice to control the amount of the recirculated exhaust gas in such a system by means of a flow control valve the opening of which varies and determines a minimum cross sectional area of an exhaust gas recirculation passageway or channel in response to a signal representing the mass flow rate of air taken into the engine. This manner of control involves a problem in that the mass flow rate of the recirculated exhaust gas does vary even when the valve opening is kept constant because the velocity of the gas flow varies with variations in the pressure difference between the upstream and downstream sections of the control valve. In other words, the magnitudes of both the exhaust gas pressure and intake vacuum are important parameters in addition to the degree of the control valve opening in controlling the amount or volume of recirculated exhaust gas.
In practical applications, however, it is quite difficult to control the recirculation of exhaust gas in correlation to both the magnitude of the intake vacuum and the aforementioned pressure difference. Especially when such a complicated manner of control is intended at relatively low engine speeds, it has been almost impossible to accomplish the intended control without impairing operational characteristics of the engine.